Diesel fuel and the method of preparing the same



Patented Dem 26, 1939 UNITED S AT S PATENT 2,184,440. 7 DIESEL FUEL AND'THE ims'rnonor PREPARING I THE SAME Bernard H. Shoemaker-and Howard B. Batchel-, der, Hammond, Ind., assignors to Standard Oil Company, Chicago, 111., a corporation of Indir ana No Drawing.

Application August 9, 1937,

Serial No. 158,140

12 Claims.

This invention relates to improvements-in high speed Diesel engine fuels and the method of obtaining the same.

In the operation of Diesel engines, in which the liquid fuel is injected directly into the cylinder,

the interval'between the time the fuel is injected and the time the fuel becomes ignited is called the fdelay period or ignition lag. Better engine performance is obtained when the delay period or ignition lag is of short duration, since the roughness of running or the Diesel knock is directly proportional tothe duration of the delay period. One of the desired properties of a Diesel fuel' is therefore [good ignition characteristics.

It is the primary object of this invention to provide a fuel, having improved ignition characteristics, for high speed Diesel engines.

It is another object of the present invention to provide a method of obtaining an improved Diesel engine fuel, having improved ignition characteristics. Other objects and. advantages of our invention .will become apparent from the following description thereof.

We have discovered that fuels,'having improved ignition characteristics, for high. speed Diesel engines, as evidenced by an increase in the cetane number, may be obtained by blendingtwo Diesel fuel distillates from different crudes, one of which is a high-sulfur crude, and treating the blend with sodium plumbite solution in the presence of a large excess of elemental sulfur.

We are awarethat Diesel fuels have heretofore been treated with doctor solution-in the presence of small amounts of sulfur. We are also aware that in the normal sweetening process the mercaptan's are converted to mercaptides,

and that the oil soluble higher molecular weight mercaptides are oxidized by sulfur to the disulfides. We are also aware that .disulfides have been addedto Diesel fuels. tinguishing features of our invention is that we treat a blend of particular stocks with sodium plumbitesolution in the presence of a large amount of sulfur, in excess of that required to sweeten the stock, but which will not result in the-presence of corrosive sulfur in the oil. We believe that by treating our fuel in this manner we obtain certain compounds heretofore not produced'in the normal sweetening process, which compounds impart to the finished product improved ignition characteristics. 7

In the knownmethods of sweetening petroleum distillatesthe following reactions are believed to take place:- I

From an inspection of the above equations it will One of the disbe seen that one atom' pif sulfur is necessary for each two mols of mercaptans sweetened. When the distillates are treated in the presence of an amount of sulfur-in excess of that required to sweeten the distillate we believe the following reactions occur:

We have discovered .that with certain kinds of stocks when the excess amount of sulfur used is approximately 7 times that theoretically required'to sweeten the product, i. e., when a: in the above equation is equal to at least 7, the finished product has much improved ignition characteristics.

In accordance with our invention a high sulfur fuel oil vfractiom for example a fuel oil fraction from Winkler crude, or a blend of about 60% to 95% of a Mid-Continent fraction having a distillation range of about 400 F. to 750 F. and

about 5% to 40% of a high sulfur fraction having a'distillation range of about 350 F. to 750 F. from a high sulfur crude. oil of the Winkler type,

which'blend has a distillation range of about ,-390 F. to 750- F. is treated with sodium plumbite in the presence of a largeexcess of sulfur, prefto sweeten such oils. The oils are settled and washed in the usual manner. g The followingspecific example is illustrative of our invention: Mid-Continent gas oil and 2384,440' JQ I E Y erably 3 to 6 times the amount normally added 15% of a gas oil from Winkler crude having the following respective characteristics were blended The characteristics of the blend areshown below:

Gravity A. P. I 35.1 Viscosity at 100 Seconds 39.0 Distillation: I

I. B. P F -420 10% F 495 50% F 540 F..- 608 E. P F 6'76 The sour oil by analysis (copper number) contained eight milligrams of mercaptan sulfur in each 100 cc. of the oil. To sweeten this oil would theoretically require four milligrams of sulfur for each 100 cc. of oil sweetened. However, 28 "milligrams of sulfur or seven times the theoretical the average value of x+1 in the formula RzSr-I-l of Equation 3 must be equal to eight since all of the sulfur added was consumed.

The blend before treating had a cetene number of about 53 and after treating in the foregoing manner'had a cetene number of about 57 showing a substantial increase in the cetene number indicating a product having'much improved ignition characteristics.

A Diesel fuel oil having improved ignition characteristics may also be obtained by treating a distillate fuel stock with sodium plumbite and an amount of sulfur in large excess of the quantity theoretically required to sweeten the stock, distilling the so-treated distillate fuel stock to obtain a desired sweetened condensate, reducing the bottoms, and adding the reduced bottoms in small amounts to a Diesel fuel oil to raise the cetane number thereof. a distillate fuel stock from a high sulfur crude, such as a distillate of the Winkler stove distillate type. Using stocks of this type. we have found it preferable to treat the same with. sodium plumbite and an excess amountof; sulfur over that required to sweeten the stock.- .We have found that from six to eight times the theoretical amount of sulfur required to sweeten the stock may be used without having corrosive sulfur present in the finished product. This indicates that instead of disulfides, other polysulfides, probably dialkyl octasulfides, are formed.

In order to avoid the formation of disulfides by air oxidation and to enhance the formation of higher poly sulfides, for example, octa sulfides, it may be desirable, prior to subjecting the distillate to treatment with sodium plumbite and excess sulfur, to remove substantially all of the air from the distillate stock and to conduct the subsequent treatment in a closed system in the absence of air. The air may be removed from the distillate stock by blowing the same with an inert non-oxygenated gas or by distilling over a few percent of the low boiling fractions.

The distillate fuel stock treated with sodium plumbite in the presence of about seven times the theoretical amount of sulfur is distilled, pref- Y erably steam distilled, to give a desired condensate, and the residue or bottoms further reduced by vacuum distillation or by fire and steam distillation to give a reduced bottom amounting from about 1% to about 6% of the original distillate fuel The reduced bottoms are then added in amounts of about 0.5% to 5%v to Diesel fuel oils to'raise the cetane number thereof.

A method of obtaining a Diesel fuel oil of improved ignition characteristics is exemplified by the following: A-high sulfur distillate, such as for example, a Winkler stove distillate or a stove distillate from a crudeoil of the Winkler type, having the inspection shown in Table I is treated with sodium plumbite and excess sulfur, and steam distilled to a 30% overhead of Winkler aviation gasoline having a distillation range of about 115 F. to 260 1".

Control+4% residue I.

. Control+2% residue II- We prefer to employ TABLI I Winkler stove distillate Degrees F.

Distillation:

Initial B. P I 120 10%- 192 0% 256 90% 317 Max 390 to a 52 cetane number Diesel fuel thefollowing results were obtained: 4v

Fuel 5 32 3 Control Control+2% residue I Control+l% residue II.

assess Control+3% residue II.

The above results show the effect of adding small amounts of reduced bottoms from a treated distillate fuel oil from a crude oil of the Winkler type.

While we have described our invention by certain specific examples we do not intend to limit the scope of our invention thereby, except insofar as the same is defined by the appended claims.

We claim:

1. The method of preparing a high speed Diesel engine fuel having improved ignition charactere istics and substantially free of corrosive sulfur which comprises treating a fuel oil distillate from a high sulfur crude oil with sodium plumbite solution and a large excess of sulfur, said sulfur used amounting to from about 3 to 6 times the theoretical amount required to normally sweeten such a distillate.

2. The method of preparing a high speed Diesel engine fuel having improved ignition characteristics and substantially free of corrosive sulfur which comprises blending a gas oil having a low sulfur content characteristic of Mid- Continent gas oil with a gas oil having a high sulfur content and treating the blend with sodium plumbite solution in the presence of a large at least 6 times the amount 'of sulfur theoretically required to. sweeten said blend, said treated blend being substantially free of corrosive sul- 4. The method of preparing a substantial corrosive sulfur-free high cetene number Diesel fuel comprising mixing60% to 95% of a Mid- Continent gas oil with 40% to 5% of a high sulfurgas oil obtained from a highsulfurcrude and treating said with sodium plumbite.

amountof sulfur normally required to sweeten said mixture.

5. The method of obtaining a high speed Diesel 5 engine fuel having improved ignition characteristics and substantially 'free of corrosive sulfur comprising mixing 60% to 95% f Mid-Continent distillate boiling within the range of about 350 F. to 750 F. with 40% to of a high sulfur distillate boiling within the range from about 350 F. to 750 F. and treating said mixture with sodium plumbite solution in the presence of sulfur, said sulfur being added in amounts at least 600% over the theoretical amount required to normally treat such a mixture.

s. The method described in claim 4 in which the high sulfur distillate is a distillate obtained from a high sulfur crude of the Wlnkler type.

7. A high cetene number high speed Diesel engine fuel obtained by the method of claim 2.

8. A high speed Diesel engine fuel having improved ignition characteristics obtained by the method of claim 5.

9. The method of preparing a high speed Diesel engine fuel having improved ignition characteristics and substantially free 'of corrosive sulfur comprising treating a distillate fuel stock ob-- tained from a high sulfur crude with sodium plumbite in the presence of sulfur, distilling the sweetened distillate fuel stock to obtain a condensate and a bottom stock, further reducing said bottom stock to give a reduced bottom amounting to about 1% to about 10% of the original distillate fuel stock and adding a small amount of said reduced bottoms to a Diesel fuel oil whereby the ignition characteristics of the latter are materlally improved.

I 2,184,440 solution in----;-the presence of about '7 times the- 10. The method of obtaining Diesel engine fuel oils having desirable ignition characteristics and.

substantially free of corrosive sulfur comprising treating a stove distillate with sodium plumbite in the presence of sulfur, distilling off about 30% of the said sweetened stove distillate to produce an overhead having aviation gasoline characteristics'and a bottom, further reducing said bottom to give a reduced bottom amounting to about 1% to about 6% of the original stove distillate and adding 0.5% to 5% of said reduced bottoms to Diesel fuel oils.

11. The method of obtaining Diesel engine fuel oils having improved ignition characteristics and substantially free of corrosive'sulfur comprising treating a stove distillate obtained from a crude oil of the Winkle: type with sodium plumbite in the presence of sulfur amounting to about 7 times the theoretical amount of sulfur required to normally sweeten such a distillate, distilling the treated stove'distillate to produce an overhead amounting to about 30% of the original stock and a bottom stock amounting to about 70% of 1 the original stock; further reducing said bottom stock by suitable means to produce a reduced bottoms amounting to about 1% to about 6% of l the original stove distillate and adding 0.5% to 

